1. Field of the Invention
The present invention relates to an ink jet head for forming an image by discharging ink (liquid) for deposition onto a recording medium, and more particularly to an ink jet head provided with a substrate bearing a discharge pressure generating element for generating a pressure for discharging ink, a flow path forming member adhered to the substrate for constituting an ink flow path, and a jointing layer for increasing the adhesion force between the substrate and the flow path forming member.
2. Related Background Art
Among the recording method employed in the printer or the like, the ink jet recording method of discharging ink from a discharge port onto a recording medium for forming a character or an image is recently employed widely as it is a non-impact recording system of low noise level capable of high-speed recording operation at a high density.
In general, the ink jet recording apparatus is provided with an ink jet head, a carriage for supporting such ink jet head, drive means for such carriage, conveying means for conveying a recording medium, and control means for controlling these components. The apparatus executing the recording operation under the movement of the carriage is called serial type. On the other hand, the apparatus executing the recording operation by the conveying operation of the recording medium, without the movement of the ink jet head, is called line type. In the ink jet recording apparatus of line type, the ink jet head is provided with a plurality of nozzles arranged over the entire width of the recording medium.
In the ink jet head, for the ink discharge pressure generating element for generating the pressure for discharging the ink droplet from the discharge port, there are known an electromechanical converting element such as a piezo element, an electrothermal converting element such as a heat generating resistor, or an electromagnetic wave-mechanical converting element or an electromagnetic wave-thermal converting element utilizing electric wave or laser light. Among these, the ink jet head of so-called bubble jet method utilizing a heat generating resistor for the ink discharge pressure generating element and inducing film boiling in the ink for generating a bubble thereby discharging ink, is effective for high-definition recording because the pressure generating elements can be arranged at a high density. Such ink jet head is generally provided with plural discharge ports, plural discharge pressure generating elements, and flow paths for guiding the ink, supplied from an ink supply system, through the discharge pressure generating elements to the discharge ports.
For forming an ink jet head by adjoining a flow path forming member for forming an ink flow path to a substrate bearing the discharge pressure generating element, there have conventionally been proposed various methods. For example, the Japanese Patent Application Laid-open No. 61-154947 discloses a method of forming a flow path pattern with soluble resin on a substrate bearing a discharge pressure generating element, then forming thereon and hardening a resin layer such as of epoxy resin so as to cover the flow path pattern, and, after the cutting of the substrate, dissolving out the soluble resin. Also the Japanese Patent Application Laid-open No. 3-184868 discloses that it is effective to employ a cationic polymerized and hardened substance of an aromatic epoxy compound as the covering resin for the flow path pattern.
In these producing methods, the adjoining of the substrate bearing the discharge pressure generating element and the flow path forming member is by the adhesion force of the resin constituting the flow path forming member.
In the ink jet head, the flow path is constantly filled with the ink in the normal state of use, so that the periphery of the adjoining portion between the substrate bearing the ink discharge pressure generating element and the flow path forming member is in contact with the ink. Therefore, if the adjoining is achieved by the adhesion force only of the resinous material constituting the flow path forming member, the adhesion of the adjoining portion may be deteriorated in time by the influence of the ink.
Also in the ink jet recording apparatus, it is recently required to execute recording on recording media of various materials and to provide the recorded image with water resistance, and weakly alkaline ink may be employed for meeting such requirements. Particularly in case of such weakly alkaline ink, it may become difficult to maintain the adhesion force between the substrate bearing the ink discharge pressure generating element and the flow path forming member over a prolonged period.
Also in so-called bubble jet head, in order to suppress damage in the heat generating resistor etc. by electroerosion caused by the ink or by cavitation at the extinction of the bubble, it is common to form an inorganic insulation layer composed for example of SiN or SiO2 and an anticavitation layer composed for example of Ta particularly on the heat generating resistor. Such Ta layer has a lower adhesion force than the SiN layer to the resinous material constituting the flow path forming member. For this reason, the flow path forming member may be peeled off from the Ta layer under severe conditions.
Such peeling of the flow path forming member from the substrate changes the shape of the flow path, thereby changing the ink discharge characteristics and detrimentally affecting the image formation. In order to prevent such phenomenon, according to the Japanese Patent Application Laid-open No. 11-348290 discloses it is effective to form an adhesion layer composed of polyetheramide resin between the substrate and the flow path forming member. According to the above-mentioned patent application, excellent adhesion can be maintained over a long period both in case of using the alkaline ink or in case of adjoining the flow path forming member on a Ta layer.
A conventional ink jet head having such adhesion layer is shown in FIGS. 20A and 20B which are respectively a horizontal cross-sectional view partly showing the vicinity of the flow path of such ink jet head and a cross-sectional view along a line 20Bxe2x80x9420B in FIG. 20A.
Such ink jet head is provided, on a substrate 51, with a flow path wall 61 and a ceiling portion (not shown) formed thereon and having a discharge port 59, by the aforementioned flow path forming member 58 of a resinous material. The discharge ports 59 are opened in opposed relationship to plural ink discharge pressure generating elements (not shown) provided on the substrate 51. The flow path wall 61 is formed in plural units in comb-tooth shape, and, between the adjacent flow path walls, there is formed a flow path for guiding the ink from the lower side of FIG. 20A onto each ink discharge pressure generating element. At the entrance of each flow path, there are formed vertically extending two pillars 62 with a predetermined gap therebetween, for example in order to prevent dust intrusion into the flow path.
The flow path forming member 58 is adjoined to the substrate 51 across an adhesion layer 56. Stated differently, the adhesion layer 56 is formed between the flow path forming member 58 and the substrate 51. In such configuration, if the adhesion layer 56 is formed over a planar area wider than the flow path forming member 58, there is formed, in the flow path, a step difference at the boundary between an area bearing the adhesion layer 56 and an area lacking the adhesion layer 56. Such step difference may complicate the flowability of the ink in the flow path and render it unstable, thereby hindering the desired stable ink flow. Also if the adhesion layer 56 is provided on the ink discharge pressure generating element, loss in the transmission of the discharge energy to the ink becomes large since the discharge energy from the ink discharge pressure generating element has to be transmitted to the ink through the adhesion layer 56. Also the discharge energy may apply a force or heat to the adhesion layer 56, thereby stimulating peeling thereof. Therefore, the adhesion layer 56 is preferably provided in a planar area excluding the area of the ink discharge pressure generating element. For this reason, the adhesion layer 56 is conventionally provided in a planar area narrower than the flow path forming member 58.
The aforementioned ink jet head, however, is associated with a drawback that the flow path forming member 58 may be peeled off by a physical stress applied thereto. Such phenomenon will be explained in the following with reference to FIGS. 21A, 21B and 33 which are respectively a lateral cross-sectional view of a conventional ink jet head, a magnified view of an adjoining portion of the flow path forming member 58 to the substrate 51, and a partial horizontal cross-sectional view of the vicinity of the flow path.
In such ink jet head, in the vicinity of the center of the substrate 51, an ink supply aperture 66 is formed by an etching process employing an ink supply aperture mask 53. On both sides of the ink supply aperture 60 on the substrate 51, in a direction perpendicular to the plane of FIG. 21A, there are arranged plural ink discharge pressure generating elements 52 and control signal input electrodes for driving these elements. On these elements there is formed a protective SiN layer 54, and an anticavitation Ta layer 55 is formed on the ink discharge pressure generating element 52. On the SiN layer 54, there is adjoined, across an adhesion layer 56, the flow path forming member 58 which constitutes the flow path wall 61 forming the flow path and the ceiling portion including the discharge port 59.
In such ink jet head, the flow path forming member 58 composed of a resinous composition may be swelled by prolonged contact with the ink. Such swelling generates, in the flow path forming member 58, a stress spreading from the center to the peripheral part, as indicated by an arrow in FIGS. 21A and 21B, whereby a stress is generated in the adjoining portion between the flow path forming member 58 and the substrate 51 from the interior toward the exterior so as to induce peeling of the flow path forming member 58. Such stress tends to be particularly concentrated in a front end portion of the flow path wall 61 in a direction toward the ink supply aperture 60. In the conventional configuration, a portion of the flow path forming member 58 is directly adjoined to the SiN layer 54 without the adhesion layer 56 therebetween in the vicinity of the front end of the liquid path wall 61 as explained in the foregoing, so that the peeling of the flow path forming member 58 may occur in such portion as illustrated in FIG. 21B.
Also in case of generation of such mechanical stress, in the portion where the flow path forming member 58 is adjoined to the Ta layer 55 across the adhesion layer 56, though the adhesion force between the flow path forming member 58 and the adhesion layer 56 is relatively large, that between the adhesion layer 56 and the Ta layer 55 is smaller in comparison, so that the peeling may occur between the adhesion layer 56 and the Ta layer 55 while the flow path forming member 58 and the adhesion layer 56 remain adjoined.
Such peeling of the flow path forming member 58, if generated in the portion of the flow path wall 61, significantly changes the flowability of ink in the flow path, thereby varying the ink discharge characteristics and detrimentally affecting the recorded image.
In order to achieve further increase in the recording speed of the ink jet recording apparatus, there is currently investigated the manufacture of a longer ink jet head having 600 to 1300 discharge ports per head. In such longer ink jet head, the flow path forming member 58 will have a larger contact area with the ink, and a large stress may be generated by swelling.
Also the ink flow is a factor causing the physical stress in the flow path forming member 58. At the ink flow into the flow path for replenishment after the ink discharge or at the ink filling into the ink jet head at the start of use thereof, the ink flow applies a physical stress to the flow path forming member 58. Such stress also tends to be concentrated in the front end portion of the flow path wall 61 in case it is formed in comb-tooth shape.
In consideration of the foregoing, the object of the present invention is to provide an ink jet head, constructed by adjoining a flow path forming member constituting an ink flow path to a substrate, capable of increasing the adjoining force of the substrate and the flow path forming member to prevent peeling thereof even in case a stress is applied to the adjoining portion between the substrate and the flow path forming member for example by swelling thereof, thereby enabling satisfactory recording operation in highly reliable manner over a long period, and a method for producing such ink jet head.
The above-mentioned object can be attained, according to the present invention, by an ink jet head comprising:
a substrate bearing a liquid discharge pressure generating element for generating energy for liquid discharge from a discharge port;
a flow path forming member adjoined on the substrate and forming a flow path communicating with the discharge port through position on the liquid discharge pressure generating element; and
an adhesion layer formed at least in a part between the substrate and the flow path forming member and having an adhesion force with respect to the substrate and the flow path forming member larger than that between the flow path forming member and the base;
wherein the adhesion layer is formed in a position where a stress generated in the flow path forming member in a direction for peeling from the substrate is concentrated and is in an area wider than the adjoining area between the flow path forming member and the adhesion layer.
Such configuration allows to increase the adhesion force between the flow path forming member and the substrate in a portion where the stress is concentrated in the flow path forming member in a direction for peeling from the substrate, thereby effectively suppressing the peeling of the flow path forming member from the substrate. In such configuration, the adhesion layer may be so formed as to overflow from the flow path forming member only in a portion where the stress is concentrated, so that the overflowing portion into the liquid flow path need not be made large thereby minimizing the influence on the flowability of the liquid.
In the ink jet head of the aforementioned configuration, there may be generated a stress by the swelling of the flow path forming member, principally in a direction from the common liquid chamber toward the peripheral portions. Consequently, the stress generated by the swelling is concentrated at the end portion of the flow path wall extending toward the common liquid chamber, in such a direction as to induce peeling of the flow path wall. Also the stress tends to be generated at such end portion of the flow path wall by the ink flow. Therefore, by forming the adhesion layer at the end portion of the flow path wall, over a planar area wider than the adjoining area between the flow path wall and the substrate, it is rendered possible to increase the adhesion force between the end portion of the flow path wall and the substrate, thereby effectively suppressing the peeling phenomenon in such portion.
In such configuration, the overflowing portion of the adhesion layer from the flow path forming member is present at the root portion of the flow path relatively distant from the discharge port for liquid discharge, thus having a relatively small influence on the liquid flowability in the flow path. In other portions of the flow path, the adhesion layer is preferably formed within an area included in the adjoining area of the flow path wall at the root side thereof, so as not to overflow from the flow path forming member. Also in case the flow path wall is very narrow in width, the adhesion layer may be dispensed with at the root side of the flow path wall. Even in such case, the flow path wall is difficult to be peeled off as the adhesion force thereof is increased by the adhesion layer at the front end portion thereof.
Also in case plural flow path walls are formed with a particularly small pitch, the adhesion layer may be formed in a belt-like shape so as to pass through the adjoining portions of the front end portions of such plural flow path walls. Such configuration allows to effectively increase the adhesion force between the front end portions of the flow path walls and the substrate by the adhesion layer of a sufficient area even for the flow path walls formed with a very small pitch.
Also in the ink jet head of the configuration of the present invention, there may be provided a pillar, composed of the flow path forming member, in the vicinity of the entrance of the flow path and in an area distant from the area of the flow path wall. For example such pillar may have a filter function for preventing entry of undesirable substance into the flow path. Also in such case, the adhesion layer may also be formed in an area passing through a planar area where the pillar is formed.
Also, such pillar need not necessarily be adjoined to the substrate and the ceiling formed by the flow path forming member. Therefore, the adhesion layer may be formed excluding the area of the pillar, or may be formed in the planar area of the pillar, independently from other areas. There may also be conceived a configuration in which the pillar extends from the ceiling, formed by the flow path forming member, toward the substrate to a position distanced from the adhesion layer, or a configuration in which the pillar extends from the adhesion layer toward the ceiling formed by the flow path forming member, to a position distanced from the ceiling.
The adhesion layer to be formed in the planar area passing through the area of the pillar can be, for example, an adhesion layer for protecting the rim of the liquid supply aperture, formed in an area surrounding the rim of the liquid supply aperture, formed in the substrate, so as to partly overflow in the liquid supply aperture.
In the ink jet head of the present invention, the adhesion layer is so formed as to overflow partially from the flow path forming member, and is preferably formed in an area excluding the area of the liquid discharge pressure generating element. In this manner the energy generated by the liquid discharge pressure generating element can be efficiently transmitted to the liquid without going through the adhesion layer. Also there can be prevented the peeling tendency of the adhesion layer induced by the energy generated by the liquid discharge energy generating element.
In the present invention, the adhesion layer can be advantageously composed of polyetheramide resin, particularly thermoplastic polyetheramide resin. Also the flow path forming member can be advantageously composed of a resinous material, particularly a cationic polymerized substance of epoxy resin.
In particular, the present invention is advantageously applicable to an ink jet head in which the discharge port is formed in a position opposed to the liquid discharge pressure generating element, and also to an ink jet head employing an electrothermal converting member as the liquid discharge pressure generating element.
For forming the ink jet head of the present invention, there is advantageously adopted a method comprising steps of:
coating the substrate with a resinous material for constituting the adhesion layer and patterning the resinous material into a predetermined planar shape thereby forming the adhesion layer;
coating thereon a soluble resinous material and patterning the soluble resinous material into a predetermined planar shape to form a flow path pattern;
coating thereon a resinous material for constituting the flow path forming member;
opening a discharge port in the resinous material for constituting the flow path forming member; and
dissolving out the resinous material constituting the flow path pattern.
In particular, the resinous material for constituting the adhesion layer can be advantageously composed of polyetheramide resin, and the layer of polyetheramide resin coated on the substrate can be advantageously patterned by oxygen plasma ashing.